1. Field of the Invention
The present invention relates in general to an automotive power plant structure which, for producing drive power and transmitting the power to driven wheels, comprises an engine part, a clutch part, a transmission part and a transfer part. More particularly, the present invention relates to a low-noise level automotive power plant structure which has high rigidity in construction to reduce the noise induced by the vibration thereof.
2. Description of the Prior Art
In conventional techniques, there are provided power plant structures of a type which is adopted in four wheel drive cars.
This type of power plant structure is essentially composed of an engine part, a clutch part, a transmission part and a transfer part.
The engine part is transversely mounted on an engine mounting frame of a vehicle body. The clutch part comprises a clutch and a clutch housing for receiving the clutch. The clutch is coaxially connected to a crankshaft of the engine part. The transmission part comprises a transmission and a transmission case for receiving the transmission. The transmission case is secured to the clutch housing and an input shaft of the transmission is coaxially connected to an output shaft of the clutch. The transfer part comprises a differential unit, a transfer and a transfer case. The transfer case receives the differential unit and the transfer. The transfer case is secured to a side face of the clutch housing. The differential unit comprises center and front differentials which transfer the drive power from the transmission to the front and rear driving axles.
However, the conventional power plant structure as mentioned hereinabove has a drawback which will be described as follows:
The power plant is generally too long because of the aligned arrangement of the transmission part relative to the clutch part and the engine part. That is, in this power plant, the transmission part, the clutch part and the engine part are arranged in tandem. This elongated structure tends to provide the power plant with an unsatisfactory rigidity. Furthermore, since the transmission case and the transfer case are not directly secured to the stoutly built engine part but to the clutch housing, the unsatisfied rigidity of the power plant becomes marked.
Low rigidity lowers a fundamental frequency of the power plant, the fundamental frequency being a frequency of vibration, at the lowest level, of the normal mode.
That is, when the engine runs, the transmission case and the transfer case tend to vibrate easily. Particularly, when the engine runs at a high speed, there arises an unpleasant noise induced by resonance due to the vibration of the power plant. Recently, the occurrence of this noise has become severe because the fundamental frequency has decreased with the advance of high speed and high power engines.